The present invention relates generally to detection of the onset of a rapid drop in a patient's blood pressure during extracorporeal blood treatments, such as hemodialysis, hemofiltration or hemodiafiltration.
The human body consists of approximately 60% water—a level which is important to maintain for survival. While it is unproblematic to provide the body with new water, disposal of surplus water is a major problem in renal patients. The task of the normal kidney is to remove superfluous fluid from the blood, such as water, urea and other waste products. The resulting urine is transferred to the bladder and finally leaves the body during urination. The kidney's second task is to regulate for example the balance of acid and base. With malfunctioning kidneys, disorders may develop in most major body organs, a syndrome called uremia. If uremia remains untreated, it will lead to death. Uremia is treated either by kidney transplantation, or some for of extracorporeal blood treatment.
During extracorporeal blood treatment it is common that the patient suffers from symptomatic hypotension (i.e. a rapid blood pressure decrease), followed by nausea, vomiting and sometimes fainting. Such an event is not only strenuous for the patient, but also requires considerable attention from the staff overseeing the treatment. Consequently, during extracorporeal blood treatment, it is highly desirable to detect the onset of symptomatic hypotension and preventing it from coming about.
In recent years, the connection between heart rate variability (HRV) and hypotension has been studied. HRV analysis has been proven to be a useful noninvasive tool for assessing information on the state of the autonomatic nervous system, and thus parasympathetic and sympathetic activity. If the HRV is analyzed in the frequency domain, the spectrum is often divided into two sub-bands: a low-frequency (LF) band, e.g. 0.04 Hz to 0.15 Hz, and a high-frequency (HF) band, e.g. 0.15 to 0.40 Hz. The effect on HRV due to changes in the autonomatic balance has been investigated in many studies, with the main conclusion that the LF band is influenced by sympathetic activity, whereas parasympathetic activity influences the HF band. Moreover, determinants of HRV in hemodialysis patients have been studied as well as autonomic dysfunction during hemodialysis.
In addition, the relationship between HRV and blood pressure during hemodialysis has been investigated. For instance, the patent document U.S. Pat. No. 4,718,891 describes an automated hemodialysis control based on this relationship. Although being silent about dialysis treatment, the published International Patent Application WO99/59466 discloses a combined electrocardiogram (ECG) and blood-pressure measuring apparatus.
Today, little is known about sequential changes in the activity of the autonomatic nervous system, which occur just before and during a hypotensive episode. So far, the major attention has been focused on the relation between the power in the LF and the HF band, the so-called LF/HF ratio, in hypotension-prone and hypotension-resistant uremic patients. It has been concluded that the LF/HF ratio can be used as a hypotension marker in patients receiving extracorporeal blood treatment, since significant increase of the LF/HF ratio is observed during extracorporeal blood treatment sessions not complicated by hypotension, whereas at the time of collapse, the LF/HF ratio fell markedly in sessions with hypotension. It has also been suggested that the LF/HF ratio may reveal differences between groups with different propensity to hypotension, and can thus give a deeper insight into the autonomatic control during extracorporeal blood treatment. Hence, the LF/HF ratio appears to be a useful index for discriminating between hypotension-prone and hypotension-resistant patients. The sympathovagal balance has also been identified as a major determinant of short-term blood pressure variability. The sympathovagal balance describes the dual, opposing effects of the sympathetic and parasympathetic nervous systems on the sinus node.
In the article, “ECG Changes and Cardiac Arrhythmias in Chronic Renal Failure Patients on Hemodialysis”, Journal of Electro-cardiology, Vol. 25, No. 4, October 1992, Shapira, O. M. et al. describe that patients with chronic renal failure frequently exhibit ECG changes and a high incidence of ventricular and supra-ventricular arrhythmias, which may be prognostically significant during and after extracorporeal blood treatment. One very important effect of cardiac arrhythmias and other beat abnormalities, which may occur during extracorporeal blood treatment, is that these events disturb the above-mentioned HRV analysis. As a result, the HRV-based techniques for predicting/detecting hypotension fail when ventricular ectopic beats (VEB) and supra-ventricular ectopic beats (SVEB) are too frequent. In such cases, the premature beats disrupt the neurocardiac modulation of the sinus rhythm and render adjacent RR-intervals useless for HRV analysis.
In the article “Detection of Hypotension during Hemodialysis using the ECG”, Computers in Cardiology 2004; Chicago, Ill., United States, Sep. 19-22, 2004, Solem, K., et al. describe a strategy for estimating a patient's propensity to hypotension at an early stage of hemodialysis based on evaluation of HRV and ectopic beat patterns.
However, there is yet no solution being capable of, on one hand, modeling the beat abnormality aspects of cardiac activity sufficiently well in order to detect, or predict, a rapid blood pressure change arising during an ongoing extracorporeal blood treatment; and on the other hand, minimizing the amount of unnecessary signal processing (i.e. relating to cardiac properties being irrelevant with regard to the patient's specific condition).